Researchers Tackle High-Altitude Engine Icing

NASA cites some 200 cases of power loss, likely from high-altitude icing, in the past 20 years. (Photo: NASA)

Over the last 20 years, the aviation industry has documented more than 200 incidents in which turbofans have lost power during high-altitude flights, according to NASA. Investigators have developed a theory that high concentrations of small ice crystals caused the loss of power, and researchers believe the phenomenon has become more common as engine companies introduce higher-bypass turbofans and airlines fly at higher altitudes. EASA certification director Norbert Lohl recently cited climate change as another possible explanation.
An international research effort led by Airbus is under way in Darwin, Australia, to better understand engine icing conditions, using a specially instrumented Falcon 20 business jet. This month, the “high-altitude ice crystals/high ice water content” flight campaign has taken the airplane into weather that produces specific icing conditions so researchers can study its characteristics. As part of the tests, a NASA-supplied probe measures the total water content of clouds containing high concentrations of ice crystals, in the vicinity of oceanic and continental thunderstorms.
Various teams concentrate, for instance, on analyzing data from the Falcon’s onboard weather radar (which normally does not detect ice crystals), capturing satellite imagery to help forecast where the aircraft might encounter the best icing conditions and using flight data to improve ice concentration prediction algorithms. “The research compiled during the flight campaign will build on or redefine what we know about ice crystal icing at high altitudes,” said Tom Ratvasky, the NASA Glenn project scientist supporting the campaign.
Separately, NASA scientists have developed a test facility that can re-create high-altitude engine icing. Researchers at the propulsion system laboratory at NASA's Glenn research center in Cleveland, Ohio, claim the facility is the first of its kind in the world. The wind tunnel can generate ice crystals at simulated altitudes of up to 40,000 feet, airspeeds up to Mach 0.80 and temperatures down to -60 degrees degrees F (-51C).
So far, the center has conducted only one test campaign, with a relatively small Honeywell ALF502-R5 turbofan. The facility cannot accommodate large engines but its promoters suggest an engine core or compressor could take the place of a full engine because icing happens in the compressor.
Engine makers cannot use the facility for certification. Nevertheless, researchers hope the data it produces can help industry with certification efforts. “With the controlled environment, we can study where and how the ice is accumulating," a NASA researcher told AIN.
In parallel, Airbus and its partners hope the Darwin campaign will provide useful information to aviation regulatory agencies.